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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Computer signal processing for ultrasonic attenuation and velocity measurements for material property characterizations

This report deals with instrumentation and computer programming concepts that have been developed for ultrasonic materials characterization. Methods that facilitate velocity and attenuation measurements are described. The apparatus described is based on a broadband, buffered contact probe using a pulse-echo approach for simultaneously measuring velocity and attenuation. Instrumentation, specimen condition, and signal acquisition and acceptance criteria are discussed. Typical results with some representative materials are presented.

Vary, A.↗
NASA NTRS1979

Compressional velocity measurements for a highly fractured lunar anorthosite

The compressional wave (V sub p) velocities in three mutually perpendicular directions have been measured in lunar sample 60025,174, lunar anorthosite. V sub p measurements were made at ambient temperature and pressure and a new technique was developed to measure the velocities because of the tremendous acoustic wave attenuation of the lunar sample. The measured velocities were all less than 1 km/sec and displayed up to a 21% departure from the mean value of the three directions. The velocities agree with seismic wave velocities determined for the lunar surface at the collection site.

Sondergeld, C. H.↗
NASA NTRS1980

Exploratory Meeting on Airborne Doppler Lidar Wind Velocity Measurements

The scientific interests and applications of the Airborne Doppler Lidar Wind Velocity Measurement System to severe storms and local weather are discussed. The main areas include convective phenomena, local circulation, atmospheric boundary layer, atmospheric dispersion, and industrial aerodynamics.

Fichtel, G. H.↗
NASA NTRS1980

Velocity measurements by laser resonance fluorescence

The photonburst correlation method was used to detect single atoms in a buffer gas. Real time flow velocity measurements with laser induced resonance fluorescence from single or multiple atoms was demonstrated and this method was investigated as a tool for wind tunnel flow measurement. Investigations show that single atoms and their real time diffusional motion on a buffer gas can be measured by resonance fluorescence. By averaging over many atoms, flow velocities up to 88 m/s were measured in a time of 0.5 sec. It is expected that higher flow speeds can be measured and that the measurement time can be reduced by a factor of 10 or more by careful experimental design. The method is clearly not ready for incorporation in high speed wind tunnels because it is not yet known whether the stray light level will be higher or lower, and it is not known what detection efficiency can be obtained in a wind tunnel situation.

She, C. Y.↗
NASA NTRS1977

Flow characteristics in an expansion tunnel as inferred from velocity measurements

A photoionization technique was used to study flow characteristics in an expansion tunnel. Vertical surveys of the axial component of flow velocity just downstream from the nozzle exit were obtained, and estimates of freestream density were inferred from the velocity measurement technique. The pitot pressure was measured and compared to the average axial component of velocity as a function of time for the two cases when air and CO2 were used as test gases. Vertical velocity and static density profiles at the nozzle exit are presented for the case when CO2 was used as test gas. Experimental results were used to determine the diameter and uniformity of the test core at the nozzle exit and the duration of the quasi-steady flow period. These data are relevant to evaluation of the suitability of operating an expansion tube as an expansion tunnel. The expansion tunnel is an expansion tube with a conical nozzle positioned at the exit of the acceleration section, so that nozzle entrance flow conditions are hypersonic and characterized by hypervelocity.

Miller, C. G.↗
NASA NTRS1982

A study of the geographic coverage properties of a satellite borne Doppler lidar wind velocity measuring system

Geographic coverage frequency and geographic shot density for a satellite borne Doppler lidar wind velocity measuring system are measured. The equations of motion of the light path on the ground were derived and a computer program devised to compute shot density and coverage frequency by latitude-longitude sections. The equations for the coverage boundaries were derived and a computer program developed to plot these boundaries, thus making it possible, after an application of a map coloring algorithm, to actually see the areas of multiple coverage. A theoretical cross-swath shot density function that gives close approximations in certain cases was also derived. This information should aid in the design of an efficient data-processing system for the Doppler lidar.

Pate, T. H.↗
NASA NTRS1990

Three component velocity measurements in an axisymmetric jet using LDA

A commercial three-component laser Doppler anemometer (LDA) has been used to acquire a detailed set of three-dimensional mean and fluctuating velocity measurements in a low-speed air jet entering a stagnant ambient, over the first 15 jet exit diameters along the jet trajectory. These data are consistent with previous measurements in axisymmetric, turbulent jets. Mean velocity and Reynolds stress data approach a self-preserving behavior by x/D equal to about 15. However, the RMS turbulence fluctuations were not self-preserving at this axial location, as expected based upon previous experimental studies. These data confirm the ability to obtain reliable three-dimensional velocity data using the present three-dimensional LDA system.

Kuhlman, John M.↗
NASA NTRS1984

Analysis of the uncertainties in velocity measurements with triple hot-wire probes

A detailed computerized sensitivity analysis of the triple hot-wire equations has been performed in order to delineate the uncertainties associated with measurements of the velocity components. Absolute and relative uncertainties for the instantaneous hot-wire outputs are calculated as functions of roll and pitch angles, based on a constant probability combination of the uncertainties in the inputs. From the results, it is concluded that the small inherent difficulties associated with the triple hot-wire data do not reflect artifacts introduced by the data processing. Fixed errors present in the V and W channels of the output are due to the nonzero measuring volume of the triple wire probe, and are entirely predictable.

Frota, M. N.↗
NASA NTRS1984

Improvement of vertical velocity measurements, part 3.4B

Vertical velocities are assumed to be measurable with vertically pointing antenna beams. An exact horizontal levelling and good phase calibration of the radar antenna system can yield real main-beam directions which do not significantly differ from calculated patterns. It is, thus, anticipated that antenna beams can be pointed exactly vertically. Because of area size and near-field limitations, VHF radar antennas have typically beam widths of more than several degrees. It is known that most of the reflectivity structures detected by vertically beaming VHF radars in the troposphere, stratosphere and lower mesosphere are aspect-sensitive. It cannot a priori be assumed that these structures are exactly horizontal. A few examples are investigated to support this statement.

Rottger, J.↗
DOE OSTI2024

Assessment of Weld Microstructure Through Sound Velocity Measurements for Power Plant Applications

Here, this research study employed an immersion-based micro-resolution ultrasonic velocity measurement technique (MUVT) to evaluate Grade 91 (9Cr-1Mo-V) steel welds. This process utilized a 20 MHz focused ultrasonic beam with a spot size of 250 µm, a 6 µm laser vibrometer spot size for detection, and an automated 3-axis raster scanner to accurately collect ultrasonic velocity data from two Grade 91 steel welds fabricated using cold metal transfer (CMT) and flux-cored arc welding (FCAW) processes. By analyzing the MUVT data, the Poisson’s ratio (υ) and modulus of elasticity (E), which are important mechanical properties for weldments, were calculated. The correlation between mechanical properties and ultrasonic velocity was examined. The results indicated that longitudinal ultrasonic velocity could effectively identify base metal, heat-affected zone (HAZ), and weld metal areas, showing a strong correlation with hardness. In particular, the distinctive V-shaped dip in velocity and hardness data across the HAZ areas of both samples highlighted changes in the microstructure of creep strength–enhanced ferritic steel welds. Importantly, the immersion-based MUVT demonstrated high accuracy in small sections of the weld, surpassing the conventional contact ultrasonic testing method in spatial resolution detection.

arc welding↗
NASA NTRS1991

Velocity measurements in a hydrogen arcjet using LIF

A new diagnostic developed to measure the axial velocity of atomic hydrogen in a 1-kW hydrogen-fueled arcjet thruster is reported. The technique is based on laser-induced fluorescence of the Balmer alpha transition (656 nm) in atomic hydrogen. A narrow-band CW ring dye laser scans the excitation spectrum permitting accurate determination of the absorption line shape and position. The velocity is derived from the Doppler-shifted line position. A spatially resolved velocity profile is presented with a peak velocity of 12.8 km/s at the arcjet centerline near the exit plane.

Liebeskind, John G.↗
NASA NTRS1991

Flow field velocity measurements for non-isothermal systems

Experimental techniques which can be potentially utilized to measure the gas velocity fields in nonisothermal CVD systems both in ground-based and space-based investigations are considered. The advantages and disadvantages of a three-component laser velocimetry (LV) system that was adapted specifically for quantitative determination of the mixed convective flows in a chamber for crystal growth and film formation by CVD are discussed. Data from a horizontal research CVD reactor indicate that current models for the effects of thermophoretic force are not adequate to predict the thermophoretic bias in arbitrary flow configurations. It is concluded that LV techniques are capable of characterizing the fluid dynamics of a CVD reactor at typical growth temperatures. Thermal effects are shown to dominate and stabilize the fluid dynamics of the reactor. Heating of the susceptor increases the gas velocities parallel to the face of a slanted susceptor by up to a factor of five.

Johnson, E. J.↗